The present invention relates to electronic assemblies and, more particularly, to anti-tombstoning structures and associated fabrication methods.
xe2x80x9cElectronic componentsxe2x80x9d, such as integrated circuits (ICs), discrete components, and passive components, can be physically and electrically coupled to a substrate such as a printed circuit board (PCB) to form an xe2x80x9celectronic assemblyxe2x80x9d. The xe2x80x9celectronic assemblyxe2x80x9d can be part of an xe2x80x9celectronic systemxe2x80x9d. An xe2x80x9celectronic systemxe2x80x9d is broadly defined herein as any product comprising an xe2x80x9celectronic assemblyxe2x80x9d.
Examples of electronic systems include computers (e.g., desktops, laptops, hand-helds, servers, Web appliances, routers, etc.), wireless communications devices (e.g., cellular phones, cordless phones, pagers, personal digital assistants, etc.), computer-related peripherals (e.g., printers, scanners, monitors, etc.), entertainment devices (e.g., televisions, radios, stereos, tape and compact disc players, video cassette recorders, camcorders, digital cameras, MP3 (Motion Picture Experts Group, Audio Layer 3) players, video games, watches, etc.), and the like.
In the field of electronic systems there is an incessant competitive pressure among manufacturers to drive the performance and quality of their equipment up while driving down production costs. This is particularly true regarding the packaging of electronic components on substrates, where each new generation of board-level packaging must provide increased performance and quality while generally being smaller or more compact in size.
A substrate typically includes a number of insulation and metal layers selectively patterned to provide metal interconnect lines (referred to herein as xe2x80x9ctracesxe2x80x9d), and a plurality of electronic components mounted on one or more surfaces of the substrate and functionally interconnected through the traces. The routing traces typically carry signals that are transmitted among the electronic components of the system.
One of the conventional ways of mounting components on a substrate is called surface mount technology (SMT). SMT components have terminals or leads (generally referred to as xe2x80x9celectrical contactsxe2x80x9d, xe2x80x9cbumpsxe2x80x9d, or xe2x80x9cpadsxe2x80x9d) that are soldered directly to the surface of the substrate. SMT components are widely used because of their compact size and simplicity of mounting.
The electrical contacts of an SMT component are coupled to corresponding electrically conductive mounting or bonding pads (also referred to as xe2x80x9clandsxe2x80x9d) on the surface of the substrate, in order to establish secure physical and electrical connections between the component and the substrate. In order to fabricate PCBs in higher densities, it is known to surface-mount certain small passive components, such as capacitors, resistors, and inductors. The resulting electronic system can be manufactured at a lower cost and in a more compact size, and it is therefore more commercially attractive.
Before SMT components are mounted on a substrate, the substrate pads are selectively coated with solder paste. Next, the component is carefully positioned or xe2x80x9cregisteredxe2x80x9d over the substrate, so that its electrical terminals are aligned with the corresponding substrate pads. Finally, in an operation known as xe2x80x9csolder reflowxe2x80x9d, the component terminals and the PCB pads are heated to a temperature that melts the solder paste, so that the terminals and pads make proper electrical and physical connections.
As will be discussed in greater detail below, mounting electronic components on currently used substrate pad structures can result in significant manufacturing defects.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a significant need in the art for apparatus and methods for mounting components to a substrate that offer relatively high density and high quality interconnections at a reasonable production cost.